Production of cellulose esters



Patented Sept. 23, 1952 PRODUCTION OF CELLULOSE ESTERS James-iosephAllen and John Arthur .Hawkes, Spondon, near Derby, England, assignorsto Celanese Corporation of America, a corporation of Delaware NoDrawing. ()riginal application October 14,

1947, Serial No. 779,838. Divided and this application December 15,1948, Serial No. 65,515. In Great Britain November 6, 1946 s Thispplication relates to-the production of cellulose esters of higher fattyacids, 1. e. of saturated or olefinic fatty acids containing at least 6carbon atoms in the molecule, and is a division of our co-pendingapplication S. No. 779,838 filed October 14,1947.

An example of a cellulose ester of a'higher fatty acid which is oftechnical importance is cellulose acetatestearate. This may be made, forexample, by treating an acetone-soluble cellulose acetate with astearylating agent, especially stearic anhydride, in the presence of anesterification catalyst and an organic diluent which will dissolve thecellulose acetate-stearate as it is formed. ;A catalyst-which gives verygood results is a mixture of zinc chloride and hydrogen chloride. When.esterification has proceeded to the desired degree the celluloseacetate-stearate is precipitated from the solution and is washed anddried.

. If a cellulose acetate-stearate of high viscosity is required thehydrogen chloride employed as catalyst is preferably neutralized beforethe cellulose acetate-stearate is precipitated from the solution. Forexample the hydrogen chloride may be neutralized by adding to thesolution sodium acetate. (In the present specification the hydrogenchloride is considered to have been neutralized when the amount ofneutralizing agent added to the solution is chemically equivalent ormore than equivalent to the amount of hydrogen chloride in thesolution,irrespective of the actual pH value of the solution afterneutralization. For example if the neutralizing agent is sodium acetatethe hydrogen chloride is considered to have been neutralized when, foreach molecular proportion of hydrogen chloride in the solution, at least1 molecular proportion of sodium acetate has been added to thesolution.) Besides giving a cellulose acetate-stearate of higherviscosity, neutralization has the further advantage of reducing oreliminating corrosion, for example of the vesselemployed for theprecipitation, and consequent contamination of the celluloseacetate-stearate with metallic impurities. Furthermore, the stability ofthe .cellulose acetateestearate to heat is improved. I

It has been found, however, that, while new. tralization withsodiumacetate gives a .productof high viscosity and good stability,italso tends to give a product having ahigher degree of color and hazethan when the-neutralization step is omitted, and for some purposes thisis undesirable. The same effect .isobserved if the sodium acetateisreplaced by.-magnesium.or ammonium 9 Claims. (Cl. 260 225) acetate or bysodium or ammonium carbonate. If the precipitated'celluloseacetate-stearate is subsequently washed with an aqueous alcohqlito freeit from contamination with stearic acid, as described in U. S. PatentNo. 2,400,494, the color and haze are considerably reduced; but when .ahydrocarbon washing composition is used, which, as described in U. S.application S. No. 116,678, filed December 16, 1946, and now abandoned,removes the contaminating stearic acid even more efficiently, the colorand haze'are notsubstantiale ly affected.

Other cellulose esters cfhigher fatty acids. may be made by similarmethods, using the :appropri ate acid anhydride, and their manufacturein! volves the same difiiculties as are described above in connectionwith the manufacture of cellulose acetate-stearate.

'It is an object of the present invention to-provide a method ofproducing cellulose-acetatestearate and other cellulose esters of'higherfatty acids wherein the hydrogen chloride usedas catalyst is neutralizedbefore the cellulose ester is precipitated; and yet a product of lowcolor-and good clarity is obtained.

In accordance with the invention, in the production of cellulose estersof higher fatty acids by causing cellulose or a cellulose derivative containing hydroxyl groups to react with an esterify ing"deriva'tive of theappropriate higherfatty acid, especially'the higher fatty acidanhydride;in the presence of zinc chloride and hydrogen chloride as catalyst andof a diluent which will dissolve the cellulose ester of the higher fattyacid as it is'formed and precipitating the cellulose ester of the higherfatty acid from the solution so obtained after neutralizing the hydrogenchloride in the solution, the hydrogen chloride is neutralized by meansof -a compound which does not introduce into the solution any metalother than zinc or any cationic radicle. (The term cationic radicle isemployed to denote a group of atoms which is a cation in aqueoussolution, e. g. ammonium or alkyl-am-monium;)' Examples of suitableneutralizing agents are zinc conipounds capable of neutralizing acids,e. g. zinc carbonate and especially zinc acetate and zinc salts of otherfatty acids (which on reaction with hydrogen chloride give zinchloride); olefine oxides, especially ethylene oxide (which on reactionwith hydrogen chloride give chlorhydrins); and normally liquid orgaseous olefines other than ethylene, especially propylene, thebutylenes and the amylenes (which react with hydrogen chlo+ r to g v mno hl r-paraifin hydrocarbons),

Mixtures of two or more neutralizing agents, e. g. mixtures of olefines,can be used if it is so desired.

In describing the invention in more detail it will be convenient againto refer specifically to the manufacture of cellulose acetate-stearate.

In one method of making cellulose acetatestearate in accordance with theinvention, dry acetone-soluble cellulose acetate is introduced into asolution of stearic anhydride in ethylene dichloride containing zincchloride and hydrogen chloride as catalyst, and the mixture is stirredor otherwise agitated until a moderately clear solution of celluloseacetate-stearate has been formed. Zinc acetate, preferably in powderform or dissolved in warm acetic acid, or ethylene oxide or propylene, abutylene or an amylene (or a mixture of two or more of these olefines)dissolved in cold ethylene dichloride, may then be added to thesolution, or ethylene oxide or one or more of the same olefines may befed under the surface of the solution which in each method is preferablywell stirred; the amount of zinc acetate or other neutralizing agentadded is at least equivalent to the hydrogen chloride. The celluloseacetate-stearate is then precipitated by adding to the solutionsufiicient hot water to cause most of the ethylene dichloride to boilofi together with any other low-boiling constitutents of the mixture andat the same time to remove from the cellulose acetate-stearate zincchloride and any other water-soluble constituents of the mixture. Theprecipitated cellulose acetatestearate is then separated from theaqueous liquid, e. g. by filtration or decantation, is washed,preferably with petrol or some other hydrocarbon composition boilingbetween about 60 and 200 C. or with an ether, and dried. Celluloseacetate-stearate made by the process of "the invention is not onlysuperior in color and clarity to cellulose acetate-stearate made by thesame process except that the hydrogen chloride is neutralized with asodium, magnesium or ammonium compound; it is also superior in color tocellulose acetate-stearate made without neutralizing the hydrogenchloride, besides having a higher viscosity and being considerably morestable to heat as, for example, in molding opera tlons.

Although the invention has been described with particular reference tocellulose acetate-stearate it may be applied to the production of highquality cellulose esters of higher fatty acids in general, bothsaturated and unsaturated. Examples of such esters are simple esters, e.g. cellulose laurate, palmitate, stearate and oleate, which can be madeby the action of the appropriate fatty acid anhydride on cellulose, andespecially mixed esters such as cellulose acetate palmitate andcellulose propionate-stearate, which can be made by the action of thehigher fatty acid anhydride on a lower fatty acid cellulose estercontaining free hydroxyl groups.

The invention is illustrated by the following examples. The "parts givenare parts by weight.

Example 1 74 parts of acetone-soluble cellulose acetate is added to asolution of 88 parts of stearic acid anhydride in 433 parts of ethylenedichloride containing as catalyst 0.18 part of zinc chloride and 0.36part of hydrogen chloride. As the reaction proceeds the temperature ofthe mixture rises to some extent and the cellulose acetatestcarateproduced eventually dissolves to form a clear solution. About 1 part offinely powdered anhydrous zinc acetate is then thoroughly stirred intothe solution. Boiling water is then added to vaporize the ethylenedichloride and precipitate the cellulose acetate-stearate, and theprecipitate is drained until a wet crude cellulose acetatestearate isobtained containing 1 part of solid to 4 parts of liquid. The wet crudeproduct is then washed batchwise with petrol at 50 0., each wash lastingfor 15 minutes, during which the petrol and ester are stirred.

The first wash is performed with :petrol which has already been used in5 previous washes, the second with petrol which has been used four timesbefore, and so on; the sixth and each succeeding wash is performed withpetrol which is initially free from stearic acid. In each case theamount of petrol used is about twice the weight of the wet crude esterbefore the first wash. After the tenth wash the cellulose acetatestearate, now substantially free from uncombined stearic acid, is driedin a current of heated air.

The extracts from the first, seventh, eighth, ninth and tenth washes arecombined, passed through a bed of fullers earth to remove colored andmetallic impurities, and distilled from an enamelled still. The lasttraces of petrol are removed by injecting live steam into the stillbase. The residue consists of stearic acid which is sufficiently pure tobe converted into stearic anhydride suitable for the production offurther cellulose acetate stearate.

Example 2 Cellulose acetate is caused to react with stearic anhydride,as described in Example 1, so as to form a clear solution of celluloseacetate-stearate in ethylene dichloride. 0.5 part of ethylene oxidedissolved in ethylene dichloride at about 0 C. is now added withvigorous stirring. Boiling Water is then added to vaporize most of theethylene dichloride and precipitate the cellulose acetate-stearate. Theprecipitate is drained and washed as described in Example 1,

Earample 3 The procedure of Example 2 is followed, except that, insteadof being added in solution in ethylene dichloride, ethylene oxide in thegas phase is fed to the bottom of the vessel containing theesterification solution, the solution being well stirred throughout,until substantially no free hydrogen chloride remains.

Example 4 The procedure of Example 2 or 3 is followed, except that theethylene oxide is replaced by about the same quantity of propylene.

Cellulose acetate-stearate prepared in accordance with these exampleshas a clarity about as good as or slightly better, and a substantiallybetter color, than cellulose acetate-stearate made by the same methodbut without neutralizing the hydrogen chloride. If the neutralization iseffected with sodium acetate or magnesium acetate the clarity isconsiderably lower. v

Having described our invention, what we desire to secure by LettersPatent is:

1. In the manufacture of mixed cellulose esters of higher and lowerfatty acids by the action of a higher fatty acid anhydride on a partialcellulose ester of a lower fatty acid having 2-3 carbon atoms in themolecule in the presence of zinc chloride and hydrogen chloride ascatalyst and of a solvent for the mixed cellulose ester in amountsufiicient to dissolve the said ester, the step of eliminating, beforeprecipitating the cellulose ester, substantially all the hydrogenchloride from the solution by adding to the solution a substanceselected from the group which consists of normally fluid olefines havingat least 3 carbon atoms in the molecule and olefine oxides.

2. In the manufacture of mixed cellulose esters of higher fatty acidsand acetic acid by the action of a higher fatty acid anhydride on anacetone-soluble cellulose acetate in the presence of zinc chloride andhydrogen chloride as catalyst and of a solvent for the mixed celluloseester in amount sufficient to dissolve the said ester, the step ofeliminating, before precipitating the cellulose ester, substantially allthe hydrogen chloride from the solution by adding to the solutionethylene oxide.

3. In the manufacture of mixed cellulose esters of higher fatty acidsand acetic acid by the action of a higher fatty acid anhydride on anacetone-soluble cellulose acetate in the presence of zinc chloride andhydrogen chloride as catalyst and of a solvent for the mixed celluloseester in amount sufilcient to dissolve the said ester, the step ofeliminating, before precipitating the cellulose ester, substantially allthe hydrogen chloride from the solution by adding to the solution anolefine having 3-5 carbon atoms in the molecule.

4. In the manufacture of cellulose acetate stearate by the action ofstearic anhydride on an acetone-soluble cellulose acetate in thepresence of zinc chloride and hydrogen chloride as catalyst and of asolvent for the cellulose acetate stearate in amount sufficient todissolve it, the step of eliminating, before'precipitating the celluloseacetate stearate, substantially all the hydrogen chloride from thesolution by adding to the solution ethylene oxide.

5. In the manufacture of cellulose acetate stearate by the action ofstearic anhydride on an acetone-soluble cellulose acetate in thepresence of zinc chloride and hydrogen chloride as catalyst and of asolvent for the cellulose acetate stearate in amount sufficient todissolve it, the step of eliminating, before precipitating the celluloseacetate stearate, substantially all the hydrogen chloride from thesolution by adding to the solution an olefine having 3-5 carbon atoms inthe molecule.

6. Process for the manufacture of mixed cellulose esters of higher fattyacids and acetic acid, which comprises causing a higher fatty acidanhydride to react with an acetone-soluble cellulose acetate in thepresence of zinc chloride and hydrogen chloride as catalyst and ofethylene dichloride in amount suflicient to dissolve lulose esters ofhigher fatty acids and acetic acid, which comprises causing a higherfatty acid anhydride to react with an acetone-soluble cellulose acetatein the presence of zinc chloride and hydrogen chloride as catalyst andof ethylene dichloride in amount sufficient to dissolve the mixedcellulose ester, then eliminating from the esterification solutionsubstantially all the hydrogen chloride by adding to the solution anolefine having 3-5 carbon atoms in the molecule, and subsequentlyprecipitating the mixed cel lulose ester from the solution.

8. Process for the manufacture of cellulose acetate stearate, whichcomprises causing stearic anhydride to react with an acetone-solublecellulose acetate in the presence of zinc chloride and hydrogen chlorideas catalyst and of ethylene dichloride in amount sufficient to dissolvethe cellulose acetate stearate, then eliminating from the esterificationsolution substantially all the hydrogen chloride by adding to thesolution ethylene oxide, and subsequently precipitating the celluloseacetate stearate from the solution.

9. Process for the manufacture of cellulose acetate stearate, whichcomprises causing stearic anhydride to react with an acetone-solublecellulose acetate in the presence of zinc chloride and hydrogen chlorideas catalyst and of ethylene dichloride in amount sufiicient to dissolvethe cellulose acetate stearate, then eliminating from the esterificationsolution substantially all the hydrogen chloride by adding to thesolution an olefine having 3-5 carbon atoms in the melocule, andsubsequently precipitating the cellulose acetate stearate from thesolution.

JAMES JOSEPH ALLEN. JOHN ARTHUR HAWKES.

REFERENCES CITED The, following references are of record in the file ofthis patent: 1

UNITED STATES PATENTS

8. PROCESS FOR THE MANUFACTURE OF CELLULOSE ACETATE STEARATE, WHICH COMPRISES CAUSING STEARIC ANHYDRIDE TO REACT WITH AN ACETONE-SOLUBLE CELLULOSE ACETATE IN THE PRESENCE OF ZINC CHLORIDE AND HYDROGEN CHLORIDE AS CATALYST AND OF ETHYLENE DICHLORIDE IN AMOUNT SUFFICIENT TO DISSOLVE THE CELLULOSE ACETATE STEARATE, THEN ELIMINATING FROM THE ESTERIFICATION SOLUTION SUBSTANTIALLY ALL THE HYDROGEN CHLORIDE BY ADDING TO THE SOLUTION ETHYLENE OXIDE, AND SUBSEQUENTLY PRECIPITATING THE CELLULOSE ACETATE STEARATE FROM THE SOLUTION. 